Question: Where is wrong in this code?

This is my code

restart; L := [];
for a from -10 to 10 do
for b from -10 to 10 do
for c from -10 to 10 do
k := (-a*b*c+a*b*z+a*c*y+b*c*x)/igcd(a*b, b*c, c*a, a*b*c); if a*b*c <> 0 then L := [op(L), [[a, 0, 0], [0, b, 0], [0, 0, c]], k*signum(lcoeff(k)) = 0] end if end do end do end do; nops(L); L

I think my code was error, because  a from -10 to 10. 

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